Resource Guarding is a common complaint among dog owners, but it can be corrected. We always recommend getting a trainer’s opinion and advice, but here are two excellent resources to help you understand and correct the problem.
Mine! A Practical Guide to Resource Guarding in Dogs by Jean Donaldson
Also by the same author:
Fight! A Practical Guide to the Treatment of Dog-dog Aggression
These books seem like great tools to make our rescues better doggie citizens!